A fundamental issue in the fabrication of semiconductor devices using elements from groups III and V is the development of surface passivation techniques on exposed surfaces to overcome leakage current due to surface formation of metastable intermediate compounds upon exposure to air. Consequently, researchers have for many years explored passivation techniques to develop quality III-V semiconductor surfaces for device processing. Such passivation techniques include thermal oxidation, wet oxidation, ion-beam irradiation, plasma oxidation, chemical anodization, and nitridation. In the case of aluminum antimonide (AlSb), this is of particular importance because the AlSb crystal surface is readily oxidized and amorphized through simple exposure to air.
The oxidation process of AlSb in air is typically a two-step process: an initial fast step and a subsequent slower step. The term “oxidation” is used to represent oxidation (e.g., Al2O3, Sb2O3, Sb2O4, and Sb2O5), hydroxidation (e.g., Al(OH)3), and hydration (e.g., Al2O3./H2O, Sb2O3.mH2O, Sb2O5.nH2O). The first step is a rapid formation of an oxidized amorphous layer, possibly about 150 Å thick. The second step is oxidation that proceeds continuously throughout the AlSb material. The continuous oxidation of AlSb is probably due to hydrolyzation rather than oxidation, i.e., the oxidation agents are mainly H2O molecules instead of O2 molecules in the atmosphere.
The formation of an amorphous oxide layer on AlSb is not a quality native oxide suitable for device fabrication. Dry and wet techniques to form quality oxide surfaces have not been attempted on single crystal AlSb. However, research efforts have examined the development of native oxides on very thin AlAsSb samples grown by molecular beam epitaxy (MBE) using the technique of wet thermal oxidation. The process is conducted in a tube furnace held at about 300° C. to about 400° C. for several hours by bubbling N2 gas through water heated at about 85° C. Characterization measurements indicated the conversion of Al and Sb into an oxide also generates an elemental Sb layer trapped between the crystal-oxide interfaces. The presence of elemental Sb between the crystal-oxide interfaces, however, is detrimental in producing a quality native oxide for surface passivation, insulating, and masking processes required for semiconductor device fabrication. It is of technological importance to develop a non-conductive oxide surface for the AlSb semiconducting compound to address significant device applications such as ambient temperature gamma-ray detection and substrate utilization for the 6.1 Å family Antimonide/Arsenide heterostructures devices.